WHITE-PINE BLISTER RUST. 73 
CONTROL OF THE WHITE-PINE BLISTER RUST. 
Significant Factors Which Determine Control. 
FACTORS IN THE FUNGUS. 
The significant features in the life history of Cronartium ribicola 
are as follows: The pyenospores are apparently f unctionless ; the 
aeciospores are not known to infect pines, but they do infect Ribes 
readily; the urediniospores are not known to infect pines, but they 
do infect Ribes; the sporidia produced by the teliospores are not 
known to infect Ribes, but they do infect pines. 
The spores are all distributed by the wind much more than by any 
other agency. The aeciospores are carried and are capable of infect- 
ing Ribes leaves miles away from their source. The urediniospores 
are distributed a number of hundred yards, but appear to lose their 
viability soon, so that infection by them is rather limited in extent. 
The sporidia produced by the teliospores appear to be distributed 
to a distance of a few hundred yards, but they are so frail that they 
soon lose viability. Infection by them is limited to 100 to 600 yards 
as a general thing, and more commonly the former than the latter 
distance. 
The fungus lives over winter most commonly by means of the 
mycelium, presumably in the needles and certainly in the bark of 
infected white pines. It occasionally overwinters by means of the 
aeciospores in cankers of pine bark or by the urediniospores on Ribes 
leaves. The aeciospores produced by the overwintered mycelium 
in the pine bark are the principal source of infection of the Ribes 
leaves each spring. The aeciospores carry the disease far and wide 
for miles to the new Ribes leaves. The urediniospores intensify 
the disease in the vicinity where it is started by the aeciospores. 
The sporidia carry the disease back to those pines which are rela- 
tively near infected Ribes bushes. 
High humidity of the air is necessary for any of the spore forms to 
germinate and to produce infection. 
FACTORS IN THE ENVIRONMENT. 
CLIMATIC FACTORS. 
. Climate may be reduced to the three most potent factors — mois- 
ture, sunshine, and wind. Cronartium ribicola is absolutely de- 
pendent upon abundant moisture for its development. Drought, 
especially if prolonged, apparently may hinder the development of 
the aecia (49, 135). Lack of moisture prevents germination of all 
the different forms of spores. It prevents or very greatly reduces 
the extent of infection on Ribes plants by aeciospores. It prevents 
the production of new generations of urediniospores, 53 and conse- 
quently prevents the abundant formation of uredinia as well as 
m Pennington, L. H. Op. cit. 
